A dynamic calculation method for geothermal reserves

Abstract

The present invention discloses a dynamic calculation method for geothermal reserves, belonging to the technical field of geothermal reserve estimation, and capable of solving the problem that the existing calculation method cannot accurately reflect the complex dynamic characteristics of geothermal reservoirs, resulting in a large error between the calculated reserve result and the actual situation. The method includes: S1, determining the current reservoir temperature at the target depth in the target area, and determining the temperature influence coefficient of the porosity of the reservoir rock in the target area according to the current reservoir temperature; S2, determining the pressure influence coefficient and the fluid influence coefficient of the porosity, and determining the current porosity of the reservoir rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; S3, determining the current geothermal reserve of the target area according to the current reservoir temperature and the current porosity. The present invention is used for the estimation of geothermal reserves.

Description

Technical Field

[0001] The present invention relates to a dynamic calculation method for geothermal reserves and belongs to the technical field of geothermal reserve estimation. Background Art

[0002] The existing calculation formula for geothermal reserves is as follows: ; ; ; ; ; ; where: is the heat stored in the heat reservoir (J); is the heat stored in the rock (J); is the water volume stored in the heat reservoir (m 3 ); is the static water reserve in the pores of the heat reservoir as of the calculation time (m 3 ); is the water volume released by the heat reservoir when the water level drops to the limit depth of the current water intake capacity (m 3 ); is the heat stored in the water (J); is the area of the calculation area (m 2 ); is the thickness of the heat reservoir (m); is the density of the heat reservoir rock (kg / m 3 ); is the specific heat of the heat reservoir rock (J / kg·°C); is the porosity of the heat reservoir rock; is the temperature of the heat reservoir (°C); is the local annual average temperature (°C); is the density of geothermal water (kg / m 3 ); is the transmissivity; is the height above the calculation starting point (m); is the specific heat of water (J / kg·°C).

[0003] The above calculation formula cannot accurately reflect the complex dynamic characteristics of the geothermal reservoir, resulting in a large error between the calculated reserve result and the actual situation. Specifically, it is manifested as: (1) This formula assumes that the temperature of the heat reservoir is fixed, which does not conform to the actual situation. In practical applications, the temperature of the heat reservoir will change with time and depth, especially during the process of geothermal development, heat transfer will cause temperature changes. (2) This formula assumes that the porosity is a constant, which does not hold in practice. With the changes in pressure, temperature, and the process of fluid loss, the porosity will change dynamically, thus affecting the calculation of geothermal reserves. This formula does not consider the impact of fluid loss on porosity and reserves. Especially during the development process, fluid loss may lead to changes in porosity, thereby affecting the available heat in the geothermal reservoir. Thus, calculate the geothermal reserves more accurately. Summary of the Invention

[0004] The present invention provides a dynamic calculation method for geothermal reserves, which can solve the problem that the existing calculation method cannot accurately reflect the complex dynamic characteristics of geothermal reservoirs, resulting in a large error between the calculated reserve result and the actual situation.

[0005] The present invention provides a dynamic calculation method for geothermal reserves, and the method includes:

[0006] S1. Determine the current geothermal reservoir temperature at the target depth in the target area, and determine the temperature influence coefficient of the porosity of the geothermal reservoir rock in the target area according to the current geothermal reservoir temperature;

[0007] S2. Determine the pressure influence coefficient and fluid influence coefficient of the porosity, and determine the current porosity of the geothermal reservoir rock according to the temperature influence coefficient, the pressure influence coefficient, and the fluid influence coefficient;

[0008] S3. Determine the current geothermal reserves of the target area according to the current geothermal reservoir temperature and the current porosity.

[0009] Optionally, the determination of the current geothermal reservoir temperature at the target depth in the target area in S1 specifically includes:

[0010] Determine the temperature distribution model of the target area according to the heat diffusion equation;

[0011] Determine the current geothermal reservoir temperature at the target depth in the target area according to the temperature distribution model.

[0012] Optionally, the determination of the temperature distribution model of the target area according to the heat diffusion equation is specifically:

[0013] Obtain the general solution of the heat diffusion equation and use the general solution as the temperature distribution model of the target area.

[0014] Optionally, the determination of the current geothermal reservoir temperature at the target depth in the target area according to the temperature distribution model specifically includes:

[0015] Obtain the initial temperature and steady-state temperature at the target depth in the target area;

[0016] Determine the current reservoir temperature at the target depth of the target area according to the target depth, the initial temperature, the steady-state temperature, and the temperature distribution model.

[0017] Optionally, determining the temperature influence coefficient of the porosity of the reservoir rock in the target area according to the current reservoir temperature in S1 specifically includes:

[0018] Calculate the first difference between the current reservoir temperature and the reference temperature;

[0019] Calculate the first product of the first difference and the coefficient of thermal expansion, and use the sum of the first product and 1 as the temperature influence coefficient of the porosity of the reservoir rock in the target area.

[0020] Optionally, determining the pressure influence coefficient of the porosity in S2 specifically is:

[0021] Determine the pressure influence coefficient of the porosity according to the current pressure at the target depth of the target area and the pore compressibility coefficient.

[0022] Optionally, determining the pressure influence coefficient of the porosity according to the current pressure at the target depth of the target area and the pore compressibility coefficient specifically includes:

[0023] Calculate the second difference between the current pressure at the target depth of the target area and the reference pressure;

[0024] Calculate the second product of the second difference and the pore compressibility coefficient, and use the difference between 1 and the second product as the pressure influence coefficient of the porosity.

[0025] Optionally, determining the fluid influence coefficient of the porosity in S2 specifically is:

[0026] Determine the fluid influence coefficient of the porosity according to the fluid loss amount per unit time in the target area and the fluid loss coefficient.

[0027] Optionally, determining the fluid influence coefficient of the porosity according to the fluid loss amount per unit time in the target area and the fluid loss coefficient specifically is:

[0028] Calculate the third product of the fluid loss amount per unit time in the target area and the fluid loss coefficient, and use the difference between 1 and the third product as the fluid influence coefficient of the porosity.

[0029] Optionally, determining the current porosity of the reservoir rock according to the temperature influence coefficient, the pressure influence coefficient, and the fluid influence coefficient in S2 specifically includes:

[0030] Calculate the fourth product of the temperature influence coefficient, the pressure influence coefficient, and the fluid influence coefficient;

[0031] Calculate the product of the fourth product and the reference porosity as the current porosity of the geothermal reservoir rock.

[0032] The beneficial effects that the present invention can produce include:

[0033] The dynamic calculation method of geothermal reserves provided by the present invention, by considering the influence of changes in formation pressure, temperature, fluid loss, and time on the porosity of geothermal reservoir rock, introducing the temperature influence coefficient, the pressure influence coefficient, and the fluid influence coefficient, makes the calculation of porosity more accurate, and further makes the calculation result of geothermal reserves more accurate.

[0034] The dynamic calculation method of geothermal reserves provided by the present invention takes into account dynamic change factors such as temperature and porosity, and uses the heat diffusion equation and the porosity optimization model to be able to reflect the changes of the geothermal reservoir in real time and provide a more accurate reserve assessment. This method combines the advantages of numerical simulation and physical models, and through the calculation means of multi-variable and multi-physical field coupling, improves the accuracy and real-time performance of geothermal reserve estimation. Description of the Drawings

[0035] Figure 1 It is a flow chart of the dynamic calculation method of geothermal reserves provided by the embodiment of the present invention. Detailed Embodiment

[0036] The following describes the present invention in detail with reference to the embodiments, but the present invention is not limited to these embodiments.

[0037] The embodiment of the present invention provides a dynamic calculation method of geothermal reserves, as Figure 1 shown, the method includes:

[0038] S1. Determine the current geothermal reservoir temperature at the target depth in the target area, and determine the temperature influence coefficient of the porosity of the geothermal reservoir rock in the target area according to the current geothermal reservoir temperature.

[0039] Among them, determining the current geothermal reservoir temperature at the target depth in the target area specifically includes:

[0040] (1) Determine the temperature distribution model of the target area according to the heat diffusion equation.

[0041] Specifically: Obtain the general solution of the heat diffusion equation and use the general solution as the temperature distribution model of the target area.

[0042] The existing formula assumes a fixed geothermal reservoir temperature , but the variation of the reservoir temperature with time and depth cannot be ignored in actual situations. Therefore, the present invention establishes a temperature distribution model to dynamically describe the temperature variation of the reservoir, considering the heat diffusion equation as: , and taking its general solution as the temperature distribution model, where represents the initial temperature, is the steady-state temperature at the target depth , represents the thermal diffusivity, is the density of the rock, is the specific heat capacity, is the thermal conductivity of the rock (thermal conductivity), a physical quantity describing the heat conduction performance of the material, which can measure the ability of heat to pass through a unit area per unit time, represents the error function, which describes the diffusion process of heat in the reservoir and the dynamic response of the temperature when it changes with time. At in the case of a small , it means that when the depth is relatively shallow or the time is relatively short, the heat diffusion has not reached the deep layer. At in the case of a large , it means that the heat has diffused to this depth and the temperature tends to be stable.

[0043] (2) Determine the current reservoir temperature at the target depth of the target area according to the temperature distribution model.

[0044] Specifically, it includes: first, obtaining the initial temperature and the steady-state temperature at the target depth of the target area; then, determining the current reservoir temperature at the target depth of the target area according to the target depth, the initial temperature, the steady-state temperature, and the temperature distribution model.

[0045] In the embodiment of the present invention, the temperature distribution model is used to calculate the current reservoir temperature at the target depth of the target area.

[0046] Since the prior art assumes that the reservoir temperature is fixed and ignores the actual situation where the reservoir temperature changes with time and depth. By introducing the heat diffusion equation, the present invention can dynamically calculate the temperature distribution and accurately reflect the temperature change in the geothermal reservoir. Especially during the geothermal development process, the temperature is a dynamically changing factor, and the heat diffusion equation can take this change into account.

[0047] Among them, determining the temperature influence coefficient of the porosity of the reservoir rock in the target area according to the current reservoir temperature specifically includes: first, calculating the first difference between the current reservoir temperature and the reference temperature; then, calculating the first product of the first difference and the temperature expansion coefficient, and taking the sum value of the first product and 1 as the temperature influence coefficient of the porosity of the reservoir rock in the target area.

[0048] The specific calculation formula is as follows:

[0049]

[0050] In the formula, is the temperature influence coefficient, is the coefficient of thermal expansion, representing the influence of temperature change on porosity; is the current temperature of the geothermal reservoir, is the reference temperature (such as the surface temperature).

[0051] High temperature often causes the rock to expand, reducing its porosity; low temperature may cause the rock to contract, increasing the porosity. This relationship can be described by the coefficient of thermal expansion . The influence of temperature on porosity is usually linear, but in some high-temperature conditions, more complex non-linear models can also be considered.

[0052] S2. Determine the pressure influence coefficient and fluid influence coefficient of porosity, and determine the current porosity of the geothermal reservoir rock according to the temperature influence coefficient, pressure influence coefficient and fluid influence coefficient.

[0053] Among them, to determine the pressure influence coefficient of porosity, specifically: determine the pressure influence coefficient of porosity according to the current pressure at the target depth in the target area and the pore compressibility coefficient.

[0054] Specifically: First, calculate the second difference between the current pressure at the target depth in the target area and the reference pressure; then calculate the second product of the second difference and the pore compressibility coefficient, and take the difference between 1 and the second product as the pressure influence coefficient of porosity.

[0055] The specific calculation formula is as follows:

[0056]

[0057] In the formula, is the pressure influence coefficient, is the pore compressibility coefficient, representing the influence of pressure change on porosity; is the current pressure, is the reference pressure (such as the surface pressure).

[0058] The porosity of the rock changes with the change of formation pressure. Usually, the greater the pressure, the rock will be compacted and the porosity will decrease. This change can be described by a linear relationship or a more complex non-linear relationship. The in the above formula is to describe the influence of pressure change on porosity, where is the pore compressibility coefficient.

[0059] Among them, the fluid influence coefficient for determining porosity is specifically: the fluid influence coefficient of porosity is determined according to the fluid loss amount per unit time in the target area and the fluid loss coefficient.

[0060] Specifically: calculate the third product of the fluid loss amount per unit time in the target area and the fluid loss coefficient, and take the difference between 1 and the third product as the fluid influence coefficient of porosity.

[0061] The specific calculation formula is as follows:

[0062]

[0063] In the formula, is the fluid influence coefficient, is the fluid loss coefficient, indicating the influence of fluid loss on porosity; is the fluid loss amount per unit time.

[0064] Among them, the fluid loss amount is related to the porosity , the current pressure , and its specific calculation formula is as follows:

[0065]

[0066] In the formula, is the permeability of the rock (unit: Darcy) under the condition of porosity , is the viscosity of the fluid (unit: Pa·s), is the flow area (unit: m 2 ), is the reference pressure (unit Pa), is the current pressure (unit: Pa), is the length of the flow path (unit: m).

[0067] Fluid loss will lead to a decrease in the available fluid in the pores, thus changing the porosity. The fluid loss amount may be related to factors such as porosity, pressure, and the permeability of the rock. Fluid loss will lead to an increase in porosity, especially during the extraction process or overexploitation process, and the change in porosity is more significant. This influence can be quantified by the fluid loss coefficient .

[0068] Among them, the current porosity of the geothermal reservoir rock is determined according to the temperature influence coefficient, the pressure influence coefficient, and the fluid influence coefficient, specifically including: first calculate the fourth product of the temperature influence coefficient, the pressure influence coefficient, and the fluid influence coefficient; then calculate the product of the fourth product and the reference porosity as the current porosity of the geothermal reservoir rock. ​​​​​

[0069] Porosity of the geothermal reservoir rock During the development process, it will change with the changes in pressure, temperature and fluid loss. The present invention optimizes the porosity through the following formula for optimization.

[0070]

[0071] In the formula: is the reference porosity (usually the porosity under the reference pressure and reference temperature ); is the pore compressibility coefficient, indicating the influence of pressure change on porosity (unit: 1 / Pa); is the current pressure (unit: Pa); is the reference pressure (such as surface pressure); is the temperature expansion coefficient, indicating the influence of temperature change on porosity (unit: 1 / ℃); is the current geothermal reservoir temperature (unit: ℃); is the reference temperature (such as surface temperature); is the fluid loss coefficient, indicating the influence of fluid loss on porosity (unit: m³ / Pa); is the fluid loss amount per unit time (unit: m³ / s).

[0072] The prior art assumes that the porosity is constant and cannot reflect the influence of pressure, temperature and fluid loss on porosity in practice. By introducing a dynamic porosity update model, the present invention can accurately calculate the dynamic change of porosity according to the changes in formation pressure, temperature, fluid loss and time, improving the accuracy of reserve calculation.

[0073] S3. Determine the current geothermal reserve of the target area according to the current geothermal reservoir temperature and the current porosity.

[0074] After determining the current geothermal reservoir temperature and the current porosity, the existing calculation formula for geothermal reserve can be used to calculate the current geothermal reserve of the target area, and the present invention does not limit the specific calculation formula.

[0075] By considering the dynamic changes of factors such as temperature and porosity, and combining the advantages of numerical simulation and physical models, the present invention achieves higher accuracy and real-time performance in geothermal reserve estimation. Compared with the prior art, the present invention can better reflect the complex characteristics of the geothermal reservoir, especially the dynamic changes during the geothermal development process, thereby effectively improving the accuracy and reliability of geothermal reserve estimation.

[0076] The present invention provides a specific calculation process for geothermal reserve, mainly including the following steps:

[0077] 1. Input the initial data.

[0078] The area of the target region calculated (unit: m²), the reservoir thickness (unit: m), the surface pressure (reference pressure, unit: Pa), the initial temperature (reference temperature, unit: °C); the geothermal water density (unit: kg / m³); the physical parameters of the heat reservoir rock: the rock density (unit: kg / m³), the specific heat of the rock (unit: J / kg·°C); the specific heat of water (unit: J / kg·°C); the fluid loss (unit: m³ / s); the reference porosity obtained through experiments , the fluid loss coefficient , the pore compressibility coefficient and the temperature expansion coefficient .

[0079] 2. Calculate the current heat reservoir temperature.

[0080] Solve the temperature distribution at each depth and time point through the heat diffusion equation , and dynamically update the current heat reservoir temperature of the reservoir using the error function model.

[0081] 3. Calculate the current porosity.

[0082] According to the actual current formation pressure , the current heat reservoir temperature and the fluid loss , dynamically update the current porosity:

[0083]

[0084] 4. Calculate the current geothermal reserve.

[0085] Use the updated current heat reservoir temperature and the current porosity to calculate the heat storage in the rock and water and . Summarize the reserve data of each region to obtain the total current geothermal reserve.

[0086]

[0087] In the formula, is the current geothermal reserve, is the heat stored in the rock, is the heat stored in the water.

[0088] 5. Dynamically update parameters.

[0089] Update the current reservoir temperature in real time over time and the current porosity , and dynamically correct the estimated value of the current geothermal reserve through numerical simulation.

[0090] Since the traditional geothermal reserve calculation formula cannot be dynamically corrected, and the present invention can continuously adjust the calculation parameters with the progress of geothermal development through numerical simulation and dynamic correction methods, providing real-time geothermal reserve estimation results, improving the real-time performance and accuracy of the estimation method.

[0091] In addition, the present invention combines the coupled calculations of multiple physical fields such as heat diffusion and porosity optimization, and can comprehensively consider the mutual influences among factors such as temperature, porosity, and fluid loss, so as to obtain a more accurate geothermal reserve estimation result.

[0092] The above are only several embodiments of the present application, and do not impose any form of limitation on the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the technical solution of the present application, makes some changes or modifications using the disclosed technical content, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for dynamic calculation of geothermal reserves, characterized in that: The method comprises: S1. Determine the current heat storage temperature of the target area at the target depth, and determine the temperature influence coefficient of the porosity of the heat storage rock in the target area according to the current heat storage temperature; S2, determining the pressure influence coefficient and the fluid influence coefficient of the porosity, and determining the current porosity of the thermal reservoir rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; S3, determining the current geothermal reserve of the target area according to the current heat reservoir temperature and the current porosity; Determining the temperature influence coefficient of the porosity of the heat reservoir rock in the target area according to the current heat reservoir temperature in S1 specifically includes: Calculating a first difference between the current thermal storage temperature and a reference temperature; The first product of the first difference and the temperature expansion coefficient is calculated, and the sum of the first product and 1 is used as the temperature influence coefficient of the porosity of the thermal reservoir rock in the target area.

2. The method according to claim 1, characterized in that The step of determining the current heat storage temperature of the target area at the target depth in S1 specifically includes: Determine the temperature distribution model of the target area according to the heat diffusion equation; The current heat reservoir temperature of the target area at the target depth is determined according to the temperature distribution model.

3. The method according to claim 2, characterized in that The temperature distribution model of the target area is determined according to the heat diffusion equation, specifically: A general solution of the heat diffusion equation is obtained, and the general solution is used as a temperature distribution model of the target area.

4. The method according to claim 2, characterized in that: Determining the current heat storage temperature of the target area at the target depth according to the temperature distribution model specifically includes: Acquiring an initial temperature and a steady-state temperature of the target area at a target depth; The current heat reservoir temperature of the target area at the target depth is determined according to the target depth, the initial temperature, the steady-state temperature and the temperature distribution model.

5. The method according to claim 1, characterized in that The pressure influence coefficient for determining the porosity in S2 is specifically: The pressure influence coefficient of the porosity is determined according to the current pressure of the target area at the target depth and the pore compressibility coefficient.

6. The method according to claim 5, characterized in that The step of determining the pressure influence coefficient of the porosity according to the current pressure of the target area at the target depth and the pore compressibility coefficient specifically includes: Calculating a second difference between the current pressure of the target area at the target depth and the reference pressure; A second product of the second difference and the pore compressibility coefficient is calculated, and the difference between 1 and the second product is used as the pressure influence coefficient of the porosity.

7. The method according to claim 1, characterized in that The fluid influence coefficient for determining the porosity in S2 is specifically: The fluid influence coefficient of the porosity is determined according to the fluid loss amount and the fluid loss coefficient of the target area per unit time.

8. The method according to claim 7, characterized in that The fluid influence coefficient of the porosity is determined according to the fluid loss amount and the fluid loss coefficient of the target area per unit time, specifically: The third product of the fluid loss amount per unit time in the target area and the fluid loss coefficient is calculated, and the difference between 1 and the third product is used as the fluid influence coefficient of the porosity.

9. The method according to claim 1, characterized in that: Determining the current porosity of the thermal reservoir rock according to the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient in S2 specifically includes: Calculating a fourth product of the temperature influence coefficient, the pressure influence coefficient and the fluid influence coefficient; The product of the fourth product and the reference porosity is calculated as the current porosity of the thermal reservoir rock.

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